The purpose of this research program has been to analyze the neural mechanisms participating in the production and regulation of cirdadian rhythms. In the next year we propose to examine the ontogeny of circadian function in the newborn rat to determine the age at which central, endogenous oscillating functions develop. We also will examine the effects of maternal behavior and other environmental influence on this function. Lesions will be made in the suprachiasmatic nuclei of the newborn rat to determine if significant plasticity exists in the development of retinohypothalamic projections and circadian functions in the developmental period. Lastly, we will initiate a detailed, quantitative analysis of the structure and connections of the suprachiasmatic nucleus. BIBLIOGRAPHIC REFERENCES: Moore, R.Y. and Traynor, M.E. Diurnal rhythms in pineal N-acetyltransferase and hippocampal noradrenaline: Effects of water deprivation, blinding and hypothalamic lesions. Neuroendocrinology 20: 250-259, 1976. Lenn, N.J., Beebe, B. and Moore, R.Y. Postnatal development of the suprachiasmatic nucleus in the rat. Cell and Tissue Research 178: 463-475, 1977.